Automatic closed-loop control of temperature in a greenhouse by regulating heating and ventilation is old in the art. In fact, other factors affecting the growth and health of the crops being grown in the greenhouse have been automatically controlled. However, in the past control has been directed to maintaining the overall greenhouse environment based upon a small number of sensors and traditional control devices such as single thermostats. Thus prior greenhouse control systems have not been plant or crop oriented control systems. They have not addressed the problems of controlling growth and plant health conditions directly at the growing bed or plant level. Unfortunately, the control of the overall greenhouse conditions, while providing adequate plant growth and health conditions at one bed, may not provide the proper conditions at another bed. This may be due to the nonuniformity of a condition, say temperature, throughout the greenhouse or the fact that different beds are planted with different crops or even that different beds planted with the same crop are at different stages in the growing cycle. Prior greenhouse control systems have not provided adequate individualized control of bed areas based upon feedback of temperature, light, and humidity conditions directly over the beds.
Irrigation and/or misting are the application of moisture to the crop or the soil. Irrigation and/or misting of greenhouse crops based upon estimated evapotranspiration has been proposed but the approach has been crudely implemented and/or not crop oriented. See, for example, "Mist Controller Plus" Operations Manual, Oglevee Computer Systems, "Effects of Different Irrigation Methods and Levels on Greenhouse Muskmellon" ACTA HORTICULTURAE 58 (1977) and "Scheduling Irrigations with Computers" Journal of Soil and Water Conservation, September-October 1969. It has been known in a theoretical way that evapotranspiration is related to vapor pressure across the plant leaf surfaces and certain resistances. See Water Relations of Plants by Paul J. Kramer (Academic Press 1983) pp. 294-297. However, applicants are unaware of any attempt to control irrigation or misting in a greenhouse environment by simply accumulating vapor pressure deficit.